Parallel robots usage as motion simulators is increasing. Among them, the Stewart robot is most commonly used. However, a properly selected 6-PUS architecture seems to potentially offer certain advantages over the popular 6-UPS structure. To prove this hypothesis, the FUM-Stewart-M450 robot is selected as a case study in this study. The parameters representing overall robot size and desired workspace are considered to be the same in both the 6-UPS and 6-PUS robots for a fair comparison. To fully define the 6-PUS robot, three performance indices, dexterity, kinetic energy and a new modified workspace index are used for optimal determination of the remaining parameters. The proposed workspace index is specifically designed for motion simulators. It not only considers the robot workspace in all 6 degrees-of-freedom but also takes into account the main feature of motion simulators motion cues, their return to home for each subsequent motion. The Pareto front is used to compare various 6-PUS designs with the FUM-Stewart-M450. The results indicate that among the optimized robots, there exists an architecture that significantly lowers maximum actuator\\\\\\\'s static and dynamic forces. This paper offers a general outline for optimization and comparison of various robot structures having combined rotational-translational motion.

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